1. Field of the Invention
This invention relates to improvements in a fuel vapor treatment device in an evaporative emission control system for preventing the escape of fuel vapors from a fuel tank of an automotive engine, and more particularly to a device, forming part of the fuel vapor treatment device, for preventing liquefied fuel from flowing to a fuel vapor absorbent.
2. Description of the Prior Art
Typically two types of fuel vapor treatment devices (canisters) have been known in the field of automotive engines (mainly of a gasoline-fueled type) to treat fuel vapor generated in a fuel tank of the engine. One of them is schematically shown in FIG. 13 and includes a fuel vapor treatment device or canister C' containing a fuel vapor absorbent M', such as activated carbon. A ventilation line L1 is provided to connect a fuel tank Ta and the canister C'. A check valve V1 is disposed in the ventilation line L1. A purge line L2 is provided to connect the canister C' and an intake air passageway K leading to the combustion chambers of the engine. A control valve V2 is disposed in the purge line L2 to control the amount of fuel vapor sucked into the intake air passageway K.
During stoppage or cruising of the vehicle, fuel vapor generated in the fuel tank T is introduced through the ventilation line L1 to the inside of the canister C' so that the fuel vapor is absorbed in the fuel vapor absorbent M'. When the vehicle cruises, air is sucked into the canister C' through a bottom opening Ca under an air sucking action of the intake air passageway K thereby purging fuel vapor absorbed in the fuel vapor absorbent M'. The purged fuel vapor flows through the control valve V2 into the intake air passageway L2. The amount of the fuel vapor to be fed to the intake air passageway L2 is regulated by the control valve V2 whose opening degree is controlled in accordance with an engine operating condition.
Another is shown in FIG. 14, in which the fuel vapor treatment device or canister C' includes a casing main body C1, with which an upper end wall C2 is integral. A fuel vapor absorbent M", such as activated carbon, is encased in the casing main body C". The upper end wall C2 is provided with an air intake pipe Ca' through which air is introduced into the casing main body C1. A liquid collecting cover W is fixedly mounted on the upper end wall C2. The upper wall of the liquid collecting cover W is provided with an inlet pipe W1 connected through a check valve to a fuel tank, and an outlet pipe W2 connected through a check valve to an intake air passageway leading to the combustion chambers of the engine. The inlet pipe W1 is located adjacent the center axis of the casing main body C" relative to the outlet pipe W2. The liquid collecting cover W is provided at its inner wall surface with a partition wall W3 extending downwardly and having a lower end positioned adjacent the upper end wall C2, and an inner cylinder W4 through which the outlet pipe W2 is in communication with a through-hole C3 formed in the upper end wall C2. Additionally, a relay pipe W5 is provided piercing the upper end wall C2 and located outside of the inner cylinder W4 and has an upper end opened to the inside space of the liquid collecting cover W.
With this arrangement, fuel vapor generated during stoppage or cruising of the vehicle is first introduced through the inlet pipe W1 into the inside space of the liquid collecting cover W and passes through a clearance between the lower end of the partition wall W3 and the upper surface of the upper end wall C2, in which high boiling point components contained in fuel vapor is separated and collected at the lower part of the liquid collecting cover W. Accordingly, only fuel vapor in gas state passes through the relay pipe W5 and introduced into the casing main body C1 to be absorbed in the fuel vapor absorbent M". In a cruising condition of the vehicle, ambient air is sucked through the air intake pipe Ca' under the suction of the intake air passageway, thereby purging fuel vapor absorbed in the fuel vapor absorbent M". The purged fuel vapor is introduced through the through-hole C3 and the outlet pipe W2 into the intake air passageway. The arrangement of FIG. 14 is disclosed in Japanese Patent Provisional Publication No. 5-278480.
However, drawbacks have been encountered in the above-discussed two types of fuel vapor treatment devices, as set forth below. The former fuel vapor treatment device of FIG. 13 is arranged such that the whole fuel vapor generated in the fuel tank is absorbed in the fuel vapor absorbent. Accordingly, the amount of fuel vapor to be absorbed in the fuel vapor absorbent is large so that the fuel vapor absorbent tends to be readily saturated with the fuel vapor, thereby providing the fear of fuel vapor releasing out of the fuel vapor treatment device through the air intake pipe Ca. Additionally, liquefied fuel (high boiling point components contained in the fuel vapor) is also absorbed in the fuel vapor absorbent M' thereby promoting the deterioration of the fuel vapor absorbent M'.
The latter fuel vapor treatment device of FIG. 14 is used in a state to vertically extend as shown in FIG. 14 so that the liquefied fuel accumulated in the liquid collecting cover W cannot be taken out of the device, although the drawbacks encountered in the former fuel vapor treatment device are hardly arisen in this fuel vapor treatment device. In order to make possible it to take out the liquefied fuel or return the liquefied fuel to the fuel tank, it is necessary to horizontally locate the canister C" itself in a manner that the inlet pipe W1 is positioned below the outlet pipe W2, and additionally the canister C" itself is disposed at a position higher than the fuel tank. Thus, there exists a considerable restriction in a setting position of the outlet pipe and an installation state of the canister itself.